Gas detection in well logging



May 9, 1961 J. H. MAY ETAL 2,983,537

GAS DETECTION IN WELL LOGGING Filed March 26, 1958 TRAP WELL HOT- WIRE GAS DETECTOR INVENTORF JOHN H. May HURSCHEL L.MflN/ZJR AGENT United States Patent GAS DETECTION IN WELL LOGGING John H. May and Hurschel L. Mann, Jr., Houston, Tex., assignors to National Lead Company, New York, N.Y., a corporation of New Jersey Filed Mar. 26, 1958, Ser. No. 724,090

r 16 Claims. (Cl. 23-232 This invention relates to an improvement in the logging of oil and gas wells, wherein drilling muds as used in the rotary method of drilling are subjected to essentially continuous analysis to determine the presence and composition of entrained gases.

In the rotary method of drilling for oil and gas, a

. drilling fluid or mud is circulated down through the drill in order to liberate any entrained gases which may have been picked up during its circulation through the well. The liberated gases arethen subjected to various methods of analysis in order to determine their composition and thus serve as an indication of potentially productive formations recently penetrated by the bit or immediately ahead of the bit.

One of the most widely used methods of analyzing the gas mixtures liberated from drilling fluids to determine their possible hydrocarbon content is the so-called hotwire gas detector. Our invention will therefore be described primarily in connection with a hot-wire method of analyzing a gas mixture but it is not to be considered as limited thereto but rather is applicable to any method of analyzing for the presence of various components of a gas mixture. A hot-wire gas detector apparatus can be conveniently designed and operated to accurately indicate the presence of minute quantities of combustible hydrocarbons in a gas stream or sample. The operation of hot-Wire gas detectors as adapted to well logging operations is described ill-considerable detail in an article, entitledfsome Recent Developments in Mud-Analysis Logging, by B. Otto Pixler, A.I.M.E. Transactions, Petroleum Division, volume 165, page 268.

' A hot-wire gas detector can be so designed that itcan operate at one or several different 'selected'temperatures,

ice

mentioned above and as described in'the above cited reference normally operates fairly satisfactorily. Any hydrocarbon gases detected in the gas samples extracted from the drilling mud will be indicative of conditions in the bore hole and particularly the formations in close proximity to the bit that have been recently penetrated or are about. to be entered. However, many drilling operations cannot be successfully conducted with conventional water-base drilling muds and in these instances it is frequently desirable to drill with oil emulsion muds. Such emulsion drilling fluids prepared by incorporating sizable quantities of oil will seriously complicate the detection of any hydrocarbons coming from the drilled formations. Oil from still other sources may frequently enter the drilling mud and result in false gas shows, for example, where an upper oil-bearing formation has been drilled and has not yet been cased off or where oil has been used in an effort to free a stuck drill pipe'or to conduct a drill stem test.

Oil from any of the above mentioned extraneous sources will vaporize to some extent when passing through the gas extracting apparatus and thus the gas stream or samples will contain a high percentage of gaseous hydrocarbons. The gas detecting apparatus will detect this high hydrocarbon content in the gas stream and thus make for considerable confusion in attempting to accurately determine the possible presence of a producing zone in formations newly penetrated by the bit.

The presence of extraneous oil in a drilling fluid has in the past frequently presented an almost insurmountable difficulty in conducting any worthwhile determination of gas in the mud. Since it is unlikely that any significant logical to base the interpretation of significant hydrocarthe desired operating temperature being easily controlled by the amount of current passing through the filament or wire. It is, of course, well known that a higher temperature is required to effect the combustion of methane than is required to burn theheavier hydrocarbons of the.

methane series. By utilizing this difference in combustion temperatures of. the various hydrocarbons and operating the hot-wire detector at differenttemperatures, it is thus readily possible to detect the relative amounts of all bydrocarbons as a group and the relative amounts of all hydrocarbons j otherf than methane. as a second group u t present in a gas stream or sample. The difference between these two values will give anindication of {the relative amountjofmethane present. 1 i

wherconventional water basefluids are used in carryink buss drillingoperatiom'the hot-wire gasdetector as bons on the variations in the relative amount of methane detected. Unfortunately, the method of determining methane by computing the difference between total hydrocarbons as indicated by the hot-wire detector when it is operated at a high temperature and the value obtained when it is operated at a somewhat lower temperature to detect all hydrocarbons other than methane breaks down giving completely unreliable indications when methane makes up only a very small fraction of the hydrocarbons present, such as would be the case where a large proportion of heavy hydrocarbons are present as the result of extraneous oil being present in the mud. Nor is it possible to successfully eliminate the heavier hydro carbons by passing the gas stream over a series of hotwire gas detectors operated at various temperatures be cause due to the relatively small catalytic surface area of the hot-wire it quickly develops localized hot spots when a large volume of gaseous hydrocarbons is passed over it.

Attempts at catalytic combustion using catalysts chosen at random have not given useableresults, because when the temperature of the catalyst is maintained low enough so that none of the methane is combusted, then the combustion of the heavier hydrocarbons is incomplete; On the other hand, if the temperature is raised high enough to insure complete combustion of the heavier hydrocar: bons thensubstantial proportions of the methane are like wise combusted. This condition makes .it impossible to effect a clean separation between these in. order to accomplish the end result desired An object of this invention is to provide a method of pre-treatment of a gas mixture for hot-wire methane detection which enables all hydrogens and hydrocarbons heavier than methane to be selectively removed without removingany of the methane.

A further object of thisaiinvention is to provide a Patented May 9, 1961 3 method of obtaining improved mud analysis logs in the presence of extraneous hydrocarbons.

Another object of this invention is to enable gaseous hydrocarbon logging to-becarried out completely automatically without the need for the services of an operator even when oil emulsion muds are, used.

Another object of this invention is to enable methane shows to be detected in the presence of what would normally be an overwhelming quantity of heavier hydrocarbons.

Another object of this invention is to provide a means of successfully carrying out mud analysis logging in the presence of oil emulsion drilling fluids.

Another object of the invention is to enable gaseous hydrocarbon detection'to be carried out successfully following the spotting of oil in the hole to free stuck drill pipe, or following a drill-stem test.

- In the drawings,

Figure 1 is an elevational view partly in section of a catalyst device in accordance with the invention, showing diagrammatically the relationship to the gas trap on the well'and a hot-wire gas detector.

Figure 2 is a horizontal section through the device of Figure -1, takenat the level indicated in Figure 1.

Generally speaking and in accordance with an illustrative embodiment of our invention, a gas sample which has been extracted from drilling fluid by known methods and in general is considerably admixed with air, is passed through a bed of a catalyst prepared in the fashion to be described below and consisting of platinum or ruthenium deposited on an alumina carrier and which is maintained at a temperature within a critical range, which has been found to eifect complete combustion of hydrocarbons heavier than methane, while combusting none of the methane which may be present. The gas mixture which has been passed through the inventive catalyst bed as described is then subjected to further analyses as by means of a'hot-wire gas detector.

The invention-may be more readily understood in connection with the drawings. In Figure 1, a gas-air mixture obtained from a gas trap 20 as known in this art is propelled by means of a pump 21 to the catalyst assembly 22 through adit tube 1, and enters the surge chamber 2 at the top of thecell. The cell body 3 is made from a solid metal block of any available metal that has good heat conducting properties such asaluminum or brass. A suitable cell can be madefrom a cylindrical metal block about four inches'in diameter and'three inches high. A well three inches in diameter is drilled to essentially the full depth of the cylindrical block. After the gas has entered the surge chamber 2, it passes through perforated distribution plate 4 and then into contact with the catalytic bed 5. After the gas has passed through thecatalytic bed, it goes through a second perforated plate 6 and enters into a second surge chamber 7 and then passes through conduit 8 to a suitable 'gas detecting apparatus 25 which may be of the hot-wire type. The top of the catalytic cell is sealed with a tight fitting metal plate 9 which is silver-soldered after the interior portions of the cell havebeen assembled. A spacer ring'15 keeps the catalyst bed in place The temperature of the catalytic cell is controlled by an. electrical heater 10 contained in a well drilled in-the body of the cell and low and high temperature thermostats 11 and 12 which are attached to the bottom of the celL Electrical power is supplied to the heater and thermostats throughjpower lead 16. The entire catalytic oxidation cell isplaced in a canister 13 which 7 is packed with an insulating material 14 such as asbesto or glass wool. The latter, is preferred. The oxidation catalystused in the practice of our invention is prepared by coatiri'ga' thin'film of 'a catalytic metal on a substrate having a high surface area per unit The catalyst used in our invention is prepared as follows: activated alumina as supplied by the Aluminum Company of America or the Reynolds Metals Company, for example, is treated with a water solution of platinum chloride or ruthenium chloride or if desired, a mixture of the two in any proportion, all as described in further detail herein below. The activated alumina carrier may be in fine granular form but the finest granulations available le-ad to undue restriction in gas flow through the catalyst bed, while the coarsest granules or pellets available, having a lesser amount of exposed gross surface, necessitate lower flow rates for complete reaction. We have found that the best size of catalyst granule or pellet is 8 to 14 mesh, as this permits an excellent rate of flow with complete catalyst interaction.

The granular or, more properly stated, pelletized alumina is carried through several steps in succession. Step No. 1 consists of soaking the alumina in a dilute aqueous solution of a volatile acid, such as a 10% acetic acid solution, for at least one hour. Dilute hydrochloric acid, e.g., 3%, is also usable. Step No. 2 consists of leaching the thus-treated pellets for an additional hour with a similar fresh acid solution. Step No. 3 consists of washing these pellets thoroughly with water. These first three steps are optional, and may be omitted in their entirety. Step No. 4 consists of drying the pellets, either as obtained from the manufacturer or having been treated by steps Nos. 1, 2 and 3 in succession, for at least two hours at a temperature range of not less than 250 F. and preferably not greater than 350 F. Step No. 5 consists in quenching the heated pellets as soon as they are removed from the. drying oven in a solution of platinum chloride or ruthenium chloride, or a mixture of these in any proportion, such as equal quantities of each, the solution con: taining preferably about /2- gram of the noble metal chloride or chlorides in 100 cubic centimeters of distilled water, this quantity being sufficient'for quenching 100 grams of the heated alumina pellets. Step No. 6 consists of draining the pellets of any residual liquid and re-heating the pellets in the 250 F. to 350- F. range for at least three hours, which has been found to insure the removal of all excess water in the pellets. The pellets as thus prepared will be found to contain approximately A gram of platinum or ruthenium or a mixture thereof per 100 grams of pellets.

As stated, the catalyst as prepared in accordance with the above teaching is incorporated into the catalyst assembly described herein above. In carrying out the invention the catalyst assembly is maintained at a temperature range of not less than 500 F. and not more than 625 F. Below the minimum figure, combustion of heavy hydrocarbons may be incomplete; while. above the maximum figure methane begins to be combusted. As a practical matter we have found it best to set the high temperature thermostat so as to operate in a temperature between aboutSSO" F. and575 F. .It will beappreciated that commercial thermostats havean ope'ratingrange, shutting off when a maximum temperature is reached and turning t on at a somewhat lower temperature. In order to extend the operating lifeof a thermostat it is desirable to space the off and on temperatures by at least 25 R, which leads to the range just given; It has been found convenientto incorporate a low temperature thermostat into the'assem bly which can-be alternatively switched in so as to oper of volume. Suitable catalytic metals are platinum and ruthenium. The substrate which we have found useful is anularor pelleted'alumin'ai ate the cell at about 230 F..at-which temperature it'will removeonlyhydrogen from.the gas stream, for those cases where it is desired to measure all the hydrocarbons in the subsequent gas detecting step. i i

Occasionally where very heavy gas shows areencountered, or where an oil is used in compounding the drillingmud which emits heavy concentrations of volatile hydrocarbons, it will be found desirable. to add oxygen to the gas mixture prior to passage thereof into the cata# lyst.assembly;2;2:so thatineither the combustion step taking place therein or in any, subsequent stages,- as for example in the hot-wire gas detector 25, will be subjected to oxygen starvation, that is, will have less oxygen present than is needed for proper combustion.

It is of interest to record some examples of catalysts without the scope of the present invention so as to indicate the unusable results obtained. For example, when a catalyst was prepared using the pelletized alumina and platinum chloride but with the solution of the latter poured on the alumina, while both at room temperature, with subsequent oven drying, it was foundnecessary to raise the temperature of the catalyst bed to 650 F. before all of the heavy hydrocarbons were combusted. At this temperature, only 15% of the methane was combusted so that the system would not enable the objects of the present invention to be accomplished. Again, where themethod of catalyst preparation which has been described in connection with the invention was carried out by using rhodium chloride instead of platinum or ruthenium chlorides, while butane began to be burned at 475 'F. it was necessary to raise the temperature to 675 F. to bring about complete combustion of the butane, and at this temperature methane was in part combusted, which again gave unusable results.

While in describing the invention specific examples and specific materials have been mentioned, it isto be understood that the invention is a broad one and should be so construed as regards the specification and the claims hereunto appended.

In the claims which follow, heavier hydrocarbons is to be taken to mean those gaseous hydrocarbons heavier than methane which occur in drilling muds under the conditions described hereinabove, viz., ethane, propane, butane, and pentane.

In the claims which follow, platinum and ruthenium chlorides are recited as these are by far the most commonly available salts for the preparation of aqueous solutions of the respective metals. This scope of this terminology is intended to include, however, direct equivalents of chlorides for the purpose at hand, such as the other halides, dinitro-diammino-platinum and the like, for the aqueous solution of the platinum or ruthenium salt is em-. ployed for the end purpose of depositing the metal itself on the alumina carrier as the eventual result of the heat treatment. i

A specific example of the invention follows: The five steps detailed hereinabove are carried out using acetic acid in step No. 1 and aqueous platinum chloride, Pt content 0.5 gm./ 100 cc., in step No. 5. The catalyst thus prepared is packed into the assembly described, and maintained at 550 F. to 575? F. An air-gas mixture from a drilling well is passed through the assembly and it is found that all the ethane, propane, butane, and hydrogen present is removed, while the methane is not.

The air-gas mixture exiting from the assembly is tested for methane on a hotwire detector.

Having described the invention, we claim: 11 The method of detecting methane in an air-gas mixture subject to containing methane, higher hydrocarbons,

and hydrogen Which comprises: maintaining a permeable bed of a catalyst consisting essentiallyof pellets of alumina which have been heated to within a range of250? F. to350 F. for at least two hours and immediately thereafter quenched with a dilute aqueous solution of chlorides chosen from the group consisting of. platinum and ruthenium chlorides and thereafter heated to within a range of 250 F. to 350 F. for at least three hours, at a catalyst bed temperature sufficiently high to completely com-bust hydrogen and higher hydrocarbons but sufficiently low as to completely fail to combust methane, permeating said air-gas mixture through said catalyst bed, while maintained within said temperature range, so as to completely combust the hydrogen and higher hydrocarbons in said mixture and thereafter analyzing said permeated air-gas mixture for methane.

2. The method of detecting methane in an air-gas mixture subject to containing methane, higher hydrocarbons; and hydrogen which comprises: maintaining a permeable bed of a catalyst consisting essentially of pellets of alumina which have been heated to within a range of 250 F. to 350 F. for at least two hours and immediately thereafter quenched with a dilute aqueous solution of chlorides chosen from the group consisting of platinum and ruthenium chlorides and thereafter heated to within a range of 250 F. to 350 F. for at least three hours, at a catalyst bed temperature of within the range of 500 F., to 625 F., permeating said air-gas mixture through said catalyst bed, while maintained within said temperature range, so as to completely combust the hydrogen and higher hydrocarbons in said mixture and thereafter analyzing said permeated air-gas mixture for methane.

3. The method of detecting methane in an air-gas mixture subject to containing methane, higher hydrocarbons, and hydrogen which comprises: maintaining a permeable bed of a catalyst consisting essentially of pellets of alumina which have been soaked in a dilute aqueous solution of a volatile acid, subsequently leached in a fresh dilute aqueous solution of a volatile acid, subsequently washed with water, subsequently heated to within a range of 250 F. to 350 F. for at least two hours and immediately thereafter quenched with a dilute aqueous solution of chlorides chosen from the group consisting of platinum and ruthenium chlorides and thereafter heated to within a range of 250 F. to 350 F. for at least three hours, at a catalyst bed temperature sufiiciently high to completely combust hydrogen and higher hydrocarbons but sufficiently low as to completely fail to combust methane, permeating said air-gas mixture through said catalyst bed, While maintained within said temperature range, so as to completely combust the hydrogen and higher hydrocarbons in said mixture and thereafter analyzing said permeated air-gas mixture for methane. 1

4. The method of detecting methane in an air-gas mixture subject to containing methane, higher hydrocarbons, and hydrogen which comprises: maintaining a permeable bed of a catalyst consisting essentialy of pellets of alumina which have been soaked in a dilute aqueous solution of a volatile acid, subsequently leached in a fresh dilute aqueous solution of a volatile acid, subsequently washed with water, subsequently heated to within a range of 250 F. to 350 F. for at least two hours and immediately, thereafter quenched with a dilute aqueous solution. of

chlorides chosen from the group consisting of platinum and ruthenium chlorides and thereafter heated to within a range of 250 F. .to 350 F. for at least three hours, at a catalyst bed temperature of within the range of 500 F. to 625 F., permeating said air-gas mixture through said catalyst bed, while maintained Within said temperature range, so as to completely combust the hydrogen and higher hydrocarbons in said mixture and thereaften analyzing said permeated air-gas mixture for methane,

5. The method of detecting methane in an air-gas mix-, ture subject to containing methane, higher hydrocarbons, and hydrogen which comprises: maintaining a'permeable, bed of a catalyst consisting essentialy of pellets of alumi-, na which have been soaked in a dilute aqueous solution .of a volatile acid for atleast one hour, subsequently leached in a fresh dilute aqueous solution of a volatile acid for at least one hour, subsequently washed with. water, subsequently heated to within a range of 250 F.

to 350, F. for at least two hours and immediately thereafter with a dilute aqueous solution of chlorides chosen from the group consisting of platinum and ruthenium chlorides and thereafter'heated to within a range of 250 F. to 350 F. for at least three hours, at a catalyst bed temperature suthciently high to completely combust hydrogen and higher hydrocarbons but sufiiciently low as to completely fail to combust methane, permeating said air-gas, mixture through said catalyst bed, while maintaincd within said temperature range, so as to completely combust the hydrogen and higher hydrocarbons in said mixture and thereafter analysing said permeated air-gas mixture for methane.

6. The process of claim 1 in which the chloride is platinum chloride.

7. The process of claim 3 in which the dilute acid is acetic acid.

8. The process of claim 3 in which the dilute acid is acetic acid and the chloride is platinum chloride.

9. The method of treating an air gas mixture subject to containing methane, higher hydrocarbons, and hydrogen so as to free the said mixture from higher hydrocarbons and hydrogen which comprises: maintaining a permeable bed of a catalyst consisting essentially of pellets of alumina which have been heated to within a range of 250 F. to 350 F. for at least two hours and immediately thereafter quenched with a dilute aqueous solution of-chlorides chosen from the group consisting of platinum and ruthenium chlorides and thereafter heated to within a range of 250 F. to 350 F. for at least three hours, at a catalyst bed temperature sufliciently high to completely combust hydrogen and higher hydrocarbons but sufficiently low as to completely fail to combust methane, and permeating said air-gas mixture through said catalyst bed, while maintained within said temperature range, so as to completely combust the hydrogen and higher hydrocarbons in said mixture.

10. The method of treating an air-gas mixture subject to containing methane, higher hydrocarbons, and hydrogen so as to free the said mixture from higher hydrocar- 4mm and hydrogen which comprises: maintaining a permeable bed of a catalyst consisting essentially of pellets of alumina which have been heated to within a range of 250 F. to 350 F. for at least two hours and immediately thereafter quenched with a dilute aqueous solution of chlorides chosen from the group consisting of platinum and ruthenium chlorides and thereafter heated to within a range of 250 F. to 350 F. for at least three hours, at a catalyst bed temperature of within the range of 500 F., to 625 F., and permeating said air-gas mixture through said catalyst bed, while maintained within said temperature range, so as to completely combust the hydrogen and higher hydrocarbons in said mixture.

' 11. The method of treating an air-gas mixture subject to containing methane, higher hydrocarbons, and hydrogen so as to free the said mixture from higher hydrocarbons and hydrogen which comprises: maintaining a permeable bed of a catalyst consisting essentially of hours and immediately thereafter quenched with a dilute.

aqueous solution of chlorides chosen from the roup consisting of platinum and ruthenium chlorides and thereafter heated to within a range of 250 F. to 350 F. for

at least three hours, at a catalyst bed temperature sufiiciently high to completely combust hydrogen and higher hydrocarbons but s'ufiiciently low as to completely fail to combust methane, and permeating said air-gas mixture through said catalyst bed, while maintained within said to containingmethane, higher hydrocarbons, and hydrogen so as to free the said mixture from higher hydro carbons and hydrogen which comprises: maintaining a permeable bed of a catalyst consisting essentially of pellets of alumina which have been soaked in a dilute aqueous solution of a volatile acid, subsequently leached in a fresh dilute aqueous solution of a volatile acid, subsequently washed with water, subsequently heated to within a range of 250 F. to 350 F. for at least two hours and immediately thereafter quenched with a dilute aqueous solution of chlorides chosen from the group consisting of platinum and ruthenium chlorides and thereafter heated to within a range of 250 F. to 350 F. for at least three hours, at a catalyst bed temperature of within the range of 500 F. to 625 F., and permeating said air-gas mixture through said catalyst bed, while maintained within said temperature range, so as to completely combust the hydrogen and higher hydrocarbons in said mixture.

13. The method of treating an air-gas mixture subject to containing methane, higher hydrocarbons, and hydrogen so as to free the said mixture from higher hydrocarbons and hydrogen which comprises: maintaining a permeable bed of a catalyst consisting essentially of pellets of alumina which have been soaked in a dilute aqueous solution of a volatile acid for at leastone hour, subsequently leached in a fresh dilute aqueous solution of a volatile acid for at least one hour, subsequently" washed with water, subsequently heated to within a range of 250 F. to 350 F. for at least two hours and immediately thereafter with a dilute aqueous solution of chlorides chosen from the group consisting of platinum and ruthenium chlorides and thereafter heated to withina range of 250 F. to 350 F. for at least three hours, at a catalyst bed temperature sufficiently high to completely combust hydrogen and higher hydrocarbons but sufliciently low as to completely fail to combust methane, and permeating said air-gas mixture through said catalyst bed, while maintained within said temperature range, so as to completely combust the hydrogen and higher hydrocarbons in said mixture.

14. The process of claim 9 in which the chloride is platinum chloride.

15. The process of claim 11 in which the dilute acid is acetic acid.

. 16. The process of claim 11 in which the dilute acid is acetic'acid and the chloride is platinum chloride.

References Cited in the file of this patent OTHER REFERENCES .Chem, Abst, vol 29, 11035, 1935.

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1. THE METHOD OF DETECTING METHANE IN AN AIR-GAS MIXTURE SUBJECT TO CONTAINING METHANE, HIGHER HYDROCARBONS, AND HYDROGEN WHICH COMPRISES: MAINTAINING A PERMEABLE BED OF A CATALYST CONSISTING ESSENTIALLY OF PELLETS OF ALUMINA WHICH HAVE BEEN HEATED TO WITHIN A RANGE OF 250*F. TO 350*F. FOR AT LEAST TWO HOURS AND IMMEDIATELY THEREAFTER QUENCHED WITH A DILUTE AQUEOUS SOLUTION OF CHLORIDES CHOSEN FROM THE GROUP CONSISTING OF PLATINUM AND RUTHENIUM CHLORIDES AND THEREAFTER HEATED TO WITHIN A RANGE OF 250*F. TO 350*F. FOR AT LEAST THREE HOURS, AT A CATALYST BED TEMPERATURE SUFFICIENTLY HIGH TO COMPLETELY COMBUST HYDROGEN AND HIGHER HYDROCARBONS BUT SUFFICIENTLY LOW AS TO COMPLETELY FAIL TO COMBUST METHANE, PERMEATING SAID AIR-GAS MIXTURE THROUGH SAID CATALYST BED, WHILE MAINTAINED WITHIN SAID TEMPERATURE RANGE, SO AS TO COMPLETELY COMBUST THE HYDROGEN AND HIGHER HYDROCARBONS IN SAID MIXTURE AND THEREAFTER ANALYZING SAID PERMEATED AIR-GAS MIXTURE FOR METHANE. 